How can i fix the lighting to make the ''glint'' looks like a perfect circle?
To make a perfectly spherical sphere, that responds well to modifiers, you need to use an Icosphere. This is a spherical mesh made from congruent triangular faces:



When using smooth shading or a subdivision modifier, there are no artifacts as all the faces are exactly the same in size and shape.

In contrast, a UV Sphere is made up in the manner of a globe, with degrees of Longitude and Latitude: